Improved wear resistance of a high-temperature component imparted by a cobalt coating

ABSTRACT

A coated high-temperature component including a cobalt coating that has a higher carbon content is provided. A layer composed of a cobalt-based alloy is applied which is known as or is similar to substrate material, to the region of the component which is subject to the wear, wherein the component preferably comprises a nickel-based alloy as substrate material, the carbon content of which is lower than that of the cobalt-based alloy. At the high operating temperatures, carbon diffuses from the coating into the base material; this is normally undesirable, but here leads to a higher carbide proportion in the substrate and therefore to a higher hardness and therefore to an increased wear resistance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/EP2015/050032, having a filing date of Jan. 5, 2015, based off of DE Application No. 102014202457.9 having a filing date of Feb. 11, 2014, the entire contents of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a high-temperature component in which use is made of a layer composed of a cobalt-based alloy in order to increase the wear resistance.

BACKGROUND

In the high-temperature range, blade or vane tips of turbine blades or vanes in particular exhibit increased wear caused by erosive material removal.

This has the effect that the tips of the rotor blades regularly have to be reshaped by various repair methods such as welding or soldering.

SUMMARY

An aspect relates to a method by means of which the wear resistance is improved in order that the maintenance intervals can be increased.

It is proposed to apply a layer composed of a cobalt-based alloy, which is known as or is similar to substrate material, to the region of the component which is subject to the wear, wherein the component preferably comprises a nickel-based alloy as substrate material, the carbon content of which is lower than that of the cobalt-based alloy. At the high operating temperatures, carbon diffuses from the coating into the base material; this is normally undesirable, but here leads to a higher carbide proportion in the substrate and therefore to a higher hardness and therefore to an increased wear resistance.

One example of a nickel-based substrate is the blade or vane material PWA1483, to which a cobalt-based alloy PWA795 is applied.

This generally leads to carbides of the MC and M23C6 type, which lead to the higher hardness and therefore to the increased wear resistance.

BRIEF DESCRIPTION

Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

FIGS. 1 and 2 show exemplary embodiments of the invention; and

FIG. 3 shows a list of superalloys.

The figures and the description represent only exemplary embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a substrate 4 which is coated.

Particularly in the case of high-temperature components such as turbine blades or vanes 120, 130, the substrate 4, 4′ (FIG. 2) is a nickel-based or cobalt-based superalloy; in particular, it is nickel-based (FIG. 3). The substrate 4, 4′ has a first carbon proportion. A metallic protective coating 7, 7′ (FIG. 2) and/or a ceramic protective coating 10, 10′ (FIG. 2) is applied to the lateral faces of the substrate 4, 4′.

The metallic protective coating 7, 7′ is preferably free of carbon (C) and has in particular the composition NiCoCrAl or NiCoCrAlX (X=Y, Re), NiCoCrAlTa, NiCoCrAlFe, NiCOCrAlYFe, NiCoCrAlYFeTa, NiCoCrAlFeTa or NiCoCrAlYTa, in particular consisting thereof. The proportions of tantalum (Ta) or iron (Fe) lie in the single-digit percentage range, in particular <=5% by weight.

Previously, the flat blade or vane tip 19, 19′ (FIG. 2) often had no coating, and therefore a free end 19 of the substrate 4, 4′ would be exposed to the increased wear.

A layer 13, 13′ (FIG. 2) composed of a cobalt-based alloy is applied to this exposed area 14, 20, 23 (FIG. 2) of the substrate 4, 4′.

This cobalt-based alloy has a higher carbon content (C) than the substrate 4, 4′, the absolute difference in the carbon content of the substrate 4, 4′ and the layer 13, 13′ being at least 0.03% by weight.

FIG. 2 shows a further exemplary embodiment, in which the tip 19′ is formed as a tip which has an outer wall 23 with a recess 20. The metallic 7′ and ceramic 10′ coatings are similarly present here, as in FIG. 1.

Likewise, a layer 13′ composed of a cobalt-based alloy is applied to the substrate 4′ in the region of the tip 19′ there 20, 23.

Without a further heat treatment of the components shown in FIGS. 1 and 2, after a certain period of use of the components at the relatively high temperatures, carbon (C) already diffuses from the cobalt-based layer 13, 13′, preferably having a thickness of 0.1 mm, into the substrate 4, 4′ after 100 hours at 1173 K-1223 K.

A ceramic layer, if appropriate in connection with the ceramic layers 10, 10′, may preferably be present on the layers 13, 13′.

The nickel-based alloy of the substrate 4, 4′ preferably comprises at least chromium (Cr), cobalt (Co), tungsten (W), aluminum (Al), titanium (Ti), optionally tantalum (Ta) and preferably no rhenium (Re) and preferably no yttrium (Y).

The cobalt-based alloy comprises at least chromium (Cr), nickel (Ni), tungsten (W), optionally tantalum (Ta), aluminum (Al), titanium (Ti) and preferably no rhenium (Re) and preferably no yttrium (Y).

Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

For the sake of clarity, it is to be understood that the use of ‘a’ or ‘an’ throughout this application does not exclude a plurality, and ‘comprising’ does not exclude other steps or elements. 

1. A high-temperature component composed of a metallic substrate of a nickel-based or cobalt-based superalloy, comprising a composition of a nickel-based alloy, wherein the substrate has a first carbon content, wherein a layer composed of a cobalt-based alloy is applied directly to an area of the substrate, said layer having a higher carbon content than the substrate.
 2. The component as claimed in claim 1, in which the layer is applied only locally, in particular in a region with increased erosion loading.
 3. The component as claimed in claim 1, in which the substrate is coated with a metallic coating and/or a ceramic coating on the metallic coating, which adjoin the area of the substrate and wherein the metallic coating comprises no carbon.
 4. The component as claimed in claim 2, in which the region represents a flat, planar tip.
 5. The component as claimed in claim 2, in which the region represents a tip with a freestanding wall.
 6. The component as claimed in claim 1, in which the absolute difference in the carbon content of the substrate and the layer is at least 0.03% by weight.
 7. The component as claimed in claim 1, in which the substrate is directionally solidified, in columnar form and is solidified in single-crystal form.
 8. The component as claimed in claim 1, in which the layer at most partially overlaps the metallic coating.
 9. The component as claimed in claim 1, in which the layer is at least 10% thinner, than the metallic coating.
 10. The component as claimed in claim 1, in which the nickel-based alloy of the substrate comprises at least chromium, cobalt, tungsten, aluminum, titanium, and optionally tantalum and wherein it contains no rhenium (Re) and no yttrium.
 11. The component as claimed in claim 1, in which the cobalt-based alloy of the layer comprises at least chromium, nickel, tungsten, and at least one of tantalum, and aluminum, titanium and no rhenium and no yttrium.
 12. The component as claimed in claim 3, in which the metallic coating comprises no carbon and comprises NiCoCrAl, NiCoCrAlY, NiCoCrAlTa, NiCoCrAlFe, NiCOCrAlYFe, NiCoCrAlYFeTa, NiCoCrAlFeTa or NiCoCrAlYTa.
 13. The component as claimed in claim 1, in which the layer has a thickness of 1 μm to 100 μm. 